The Prototype
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Allis-Chalmers produced the HD-21 from 1954 to 1969; and to 1975
with a change in body style and specs as HD-21B. The HD-21 model
included seven different variations of design: different body
styling, power ratings, weight, air-filter canister placement.
The HD-21 was the first Allis-Chalmer's model to use it's own
manufactured engine based on the Buda diesel and not on Detroit
diesel truck engine. Equipped with a 6 cylinder supercharged engine
producing between 204 fwhp (1954 models) to 273 fwhp for 1963
model. They weighed in at 44,000 lbs (1954) to 57,100 lbs (1969
model) without any blade attachment. This means a 70-ton railroad
flat car can carry a maximum of 2-3 tractors, depending on loading
space and any additional attachments.

Historical
Context -
The HD-21 directly competed with the Cat D-8. The HD-21 was a
little cheaper in cost to acquire than an equivalent Cat machine.
It became Allis-Chalmers all time best seller. The HD-21 was equipped
with superior track bearings that kept out the dirt which the
Caterpillar finally adopted in 1958. The HD-21 had a difficult
to use manual transmission prior to their all power shift transmission
which came later. Until the 1960, the dozer model blade was operated
by cable and winch. From the 1960's on, Allis-Chalmers incorporated
a hydraulically operated blade. The production of HD-21 pre-dated
the 1975 OSHA law that required mandatory roll over protection
(canopy. However, owner-operators and contractors sometimes added
an after market canopy. In 1975, Fiat SpA took over Allis-Chalmers
line of tractors that was rebranded under the Fiat-Allis name.

Wheels of
Time Custom Editions Model -

HD-21 Crawler
Kit is especially like how they are handled on railroad flatcars.
The Crawler Kit consists of three piece (body, right side and
left side treads) high quality urethane resin castings in neutral
gray. Exhaust pipe is made of 3D printed acrylic. Assembly is
required!

HD-21 Dozer
Kit consists of body, right side and left side treads. Made of
high quality urethane resin casting in neutral gray. Highly detailed
two-piece blade (for easy installation on tractor), exhaust pipe
and hydraulic cylinders in 3D printed acrylic. Assembly is required!

Requires
washing model in dish soap, rinsing in water and letting it dry
to remove any model oil release. The 3D printed acrylic should
be washed in Simple Green and gently scrubbing with a toothbrush
to remove any wax. Then rinsed thoroughly in water.